Control System

ABSTRACT

A control system is described that comprises a manifold, at least one valve device operable to control the delivery of fluid from the manifold, and a drive member located within the manifold and rotatable to control the operation of the at least one valve device.

This invention relates to a control system. For example, the controlsystem may form part of a fuel system for use in the supply of fuel toan aircraft engine. In one particular example, the invention relates toa fuel system permitting control over the fuel staging system of such anengine.

It is known to provide an engine with a fuel system including a seriesof pilot valves and a series of main valves, or a series of valveshaving pilot and main delivery modes. In such arrangements it isnecessary to provide a control arrangement operable to control which ofthe valves are operable, or to control the delivery modes of the valves,at a given time to ensure that fuel is correctly delivered to theengine.

U.S. Pat. No. 4,036,246 describes a fuel system in which a series oflinkages are provided to control the operation of the valves. Thelinkages together form a unison ring. The linkages are movable by anappropriate actuator. In many arrangements the linkages are locatedexternally but, in the arrangement of U.S. Pat. No. 4,036,246, they arelocated within the manifold used to deliver fuel to the valves.

The use of linkages in controlling the operation of the valves resultsin the introduction of a degree of hysteresis and lost motion into thesystem which is undesirable. Furthermore, in the harsh environment of anaircraft engine fuel supply system, this hysteresis and lost motion iseven more pronounced due to temperature mismatch and vibratory effects.It is an object of the invention to provide a control system, forexample suitable for use in a mechanically actuated fuel system, ofimproved stiffness that is less susceptible to the effects oftemperature and vibration.

According to the present invention there is provided a control systemcomprising a manifold, at least one valve device operable to control thedelivery of fluid from the manifold, and a drive member located withinthe manifold and rotatable to control the operation of the at least onevalve device.

The control system may comprise part of a fuel system, for example foran aircraft engine, the manifold comprising a fuel manifold from whichfuel is delivered, in use, via the valve devices. However, the inventionis also applicable to other control systems.

Preferably, the manifold further houses at least part of an input geararrangement whereby the drive member is rotated. An input drive shaftmay be provided to transmit rotary motion from a motor to the drivemember and/or input gear arrangement. The input drive shaft may belocated within a fuel supply line whereby fuel is supplied to themanifold, thereby negating the need for fuel/air dynamic sealarrangements. Alternatively, the input drive shaft may pass through aseal arrangement into the manifold and/or input gear arrangement.

The motor may be an electrically driven motor. Alternatively, it maycomprise a hydraulic motor driven, for example, using pressurised fuel.

The manifold preferably houses a series of further drive members, oralternatively one continuous drive member, and gear arrangementsarranged to form a drive train preferably in the form of a continuousloop. Each gear arrangement is preferably further arranged to transmitrotary motion to one or more of said valve devices.

A sensor may be provided to monitor the rotary position of the drivemember, the input drive shaft and/or the motor to provide an outputsignal representative of the operating mode of the valve devices.Additional sensors may be provided to monitor the positions of the valvedevices.

Preferably there is a continuous flow of fuel through the valve devicesat all engine operating conditions, thereby providing a means ofmaintaining the temperature of the valve devices at an acceptable level.

The invention will further be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1, which is a diagram illustrating a fuel system in accordance withone embodiment of the invention; and

FIG. 2 is a diagram illustrating a control system in accordance withanother embodiment.

The fuel system illustrated in FIG. 1 comprises a hydro-mechanical unit(HMU) 10 arranged to supply fuel through a supply line 12 to a fuelmanifold 14. The HMU 10 may take a range of forms, for example it maycomprise a high pressure fuel pump arranged to supply fuel through ametering valve, the operation of which is controlled to control the rateat which fuel is supplied to the supply line 12. A spill valvearrangement may be incorporated into the HMU 10 to allow excess fuel tobe returned to inlet side of the high pressure pump. Fuel systems ofthis general type are well known and so the HMU 10 will not be describedin further detail.

The manifold 14 communicates via a series of staging valve lines 16 witha series of staging valves 18. Each staging valve 18 is operable, inthis embodiment, to supply fuel through a series of pilot outletopenings and a series of main outlet openings, the staging valves 18incorporating a control mechanism whereby certain of the outlet openingscan be closed such that, for example, fuel can be delivered in a pilotdelivery mode only. A number of valve designs of this general type areknown, so no further description thereof is included herein. However,the design of the valves is such that there is continuous flow of fuelthrough the valves at all engine operating conditions thus ensuring thatthe temperature of the valves is maintained at an acceptable level toprevent fuel degradation.

Located within the manifold 14 is a series of rotatable drive members 20in the form of flexible drive shafts. Alternatively, one continuousrotatable drive member could be located within the manifold in the formof one continuous flexible drive shaft. The drive shaft or shafts arearranged to be rotated, ill use, about their longitudinal “axes”, andheld against significant “radial” movement. The flexible drive shaftsare of high torsional stiffness and may be of the type described in U.S.Pat. No. 4,112,708. The drive members 20 are interconnected with oneanother by means of gear arrangements 22, the drive members 20 and geararrangements 22, together forming a drive train in the form of acontinuous loop extending about the entire manifold 14. The geararrangements 22 transmit rotary motion between the adjacent members 20and may take a range of forms. For example they may comprise worm/wheeltype arrangements or spur/bevel gear arrangements. The gear arrangements22, as well as transmitting rotary motion between adjacent ones of thedrive members 20, are further arranged to drive a series of outputshafts 24 for rotation, the output shafts 24 being located withinrespective ones of the staging valve lines 16. The output shafts 24 areconnected to the control mechanisms of respective ones of the stagingvalves 18 and are arranged such that rotation of the drive members 20which is transmitted through the gear arrangements 22 to the outputshafts 24 controls the mode of operation of each of the staging valves18.

The fuel system illustrated in FIG. 1 further comprises a hydraulicmotor 26 arranged to be driven using fuel under pressure. An input driveshaft 28 interconnects the motor 26 and an input one of the geararrangements 22, and it will be appreciated that operation of the motor26 can thus be used to control the rotary positions of the drive members20, gear arrangements 22, output drive shafts 24, and hence theoperating modes of the staging valves 18. In the arrangementillustrated, the input drive shaft 28 passes directly into one of thegear arrangements 22, through a suitable sealing arrangement provided inthe gear arrangement 22 and/or manifold 14. However, arrangements arepossible in which the input drive shaft 28 is housed within a fuel lineconnected to the manifold 14, for example in some arrangements the inputdrive shaft 28 may extend through part of the supply line 12 and intothe manifold 14. This would advantageously negate the need for asuitable fuel/air dynamic sealing arrangement.

In the arrangement illustrated in FIG. 1, the motor 26 comprises ahydraulic gear motor, the operation of which is controlled by aservo-valve and torque motor arrangement 38 hereinafter referred to asthe control valve 38. The motor 26 is connected between first and secondoutputs of the control valve 38 via respective fuel lines 30 and 36.These fuel lines 30, 36 are then connected via a fixed orificearrangement 34 to the supply line 12, via a line 32, which is held at apressure P1 equal to or substantially equal to the fuel pressure atwhich fuel is supplied by the HMU 10.

A servo-pump 40 is arranged to pressurise a quantity of fuel from theline 12 to an increased pressure P2, fuel from the servo-pump 40 beingsupplied to the control valve 38. This increased pressure is required toprovide satisfactory control of the motor 26 via the control valve 38.As well as controlling the operation of the motor 26, the control valve38 and fixed orifice arrangement 34 ensure that adequate flow of fuel ismaintained through the fuel lines 30, 36 at all engine operatingconditions. This ensures that the temperature of the fuel system, and inparticular that part of the fuel system which is located in the hightemperature core zone of the engine, is maintained at an acceptablelevel, thus minimising the risk of fuel degradation. A pressure limitingvalve 42 is connected between the output of the servo-pump 40 and theline 12 to prevent the pressure P2 rising to an unacceptably highpressure.

In use, depending upon the operation of the control valve 38, therespective pressures P3 and P4 in the fuel lines 30 and 36 are adjustedto control the operation of the motor 26. For example, with the controlvalve 38 operated such that P3 is greater than P4 the motor 26 rotatesin a first direction. Such rotation of the motor 26 is transmitted tothe staging valves 18 as described hereinbefore and is used to drive thestaging valves 18 from, for example, a pilot operating mode to a mainoperating mode. In another operating mode of the control valve 38, P3 isless than P4 resulting in rotation of the motor 26 in a second, oppositedirection. Such rotation is transmitted to the staging valves 18resulting in the staging valves 18 returning from, for example, the maindelivery mode to the pilot delivery mode. During certain operatingconditions continued operation of the servo-pump 40 may result in thepressure P2 rising to the point at which the pressure limiting valve 42opens to prevent the pressure P2 rising to an excessively high level.

A sensor 44 is provided to monitor the operation of the motor 26. Bysensing the position of the motor 26 it will be appreciated that asignal representative of the position or operating mode of the stagingvalves 18 can be produced. This signal is used by an Engine Control Unit(not shown) in conjunction with known engine control loop stagedcombustion algorithms (ie pilot/mains flow split calculations) toprovide a control signal to the control valve 38 that is required inproviding the necessary control of the operation of the motor 26,thereby permitting accurate control over the staging valves 18.

In normal operation, it will be appreciated that the fuel system willspend considerable periods of time in conditions in which it is notdesired to switch the staging valves 18 between their pilot and mainoperating modes. Although, desirably, the motor 26 will not move duringthese periods, in practise it is likely that the control valve 38 willbe constantly or regularly changing position, holding the pressures P3and P4 at substantially the same level. In practise, there will be someperiods where P3 is slightly greater than P4 and so the motor operatesslowly in the first direction, and other periods where P3 is slightlybelow P4 and during these periods the motor 26 will operate slowly inthe second direction. The nature of the gear arrangement 22 ispreferably such that these small perturbations in the rotation of themotor 26 cause little if any adjustment in the operating modes of thevalves 18.

It will be appreciated that, in use, there is sufficient pressuredifference (P3-P4) across the motor 26 (for example approximately 200psid) to drive the motor 26 in the valve opening direction, and therebyensure that the system operates reliably. A lower pressure difference(P4-P3) driving the motor 26 in the valve closing direction issufficient to ensure reliable valve movement as the staging valves 18will typically include springs biasing them towards their closedpositions. Further, in the event of a loss of electrical power to thesystem, the control valve 38 is biased to ensure that the motor 26 isdriven in the valve closing direction.

The arrangement described hereinbefore is advantageous compared to knownarrangements in that the number of fuel lines provided in the hightemperature core zone of the engine is reduced, and there is continuousflow of fuel in the remaining lines, thereby avoiding fuel linescontaining stagnant fuel in a high temperature environment, and hencenegating the need of an additional requirement for fuel cooling. Thelocation of the drive members 20 within the manifold 14 and also theinput drive shaft 28 extending through part of the supply line 12 andinto the manifold 14 avoids the necessity of providing dynamic fuel/airseals in the high temperature core zone of the engine. Further, theprovision of the drive members 20 and gear arrangements 22 in the formof a continuous loop results in the system being of reduced sensitivityto single point failures in that, for example, continued operation ofthe staging valves 18 may be achievable despite the failure of, forexample, one of the drive members 20. In addition, the provision of thesensor 44 permits accurate, closed loop control over the operation ofthe staging valves.

The control mechanisms of the staging valves 18 may take a range offorms. Where a rotary input is required this may be derived directlyfrom the rotation of the output drive shafts, conveniently via agearbox. Where a linear input is required, any suitable rotary to linearconversion device may be used, for example a ball screw-type device, toconvert the rotary motion of the output drive shaft to the linear motionof the staging valve 18. In either case, down gearing may be achieved atthis point.

A number of modifications and alterations may be made to the arrangementdescribed hereinbefore. For example, rather than use a hydraulicallydriven motor to control the rotation of the drive members 20, anelectrically driven motor could be used. Where the input drive shaft islocated within a fuel line, then a fuel drain line may be connected tothe motor to permit the escape of fuel therefrom. Another possibility isto provide a dedicated input gear arrangement rather than adding thisfunctionality to one of the gear arrangements used to drive the outputdrive shafts. It may, alternatively, be possible to incorporate themotor into the manifold 14. Further, although the arrangement describedhereinbefore makes use of staging valves 18 switchable between pilot andmain operating modes, it will be appreciated that separate pilotinjectors and main injectors may be provided, control over the operationof which is achieved using a system similar to that describedhereinbefore. Furthermore, it is recognised that the arrangement of adrive member located in a pipe and rotatable to control the operation ofat least one output device could be applied to an actuator controlsystem, for example the normally hydraulically operated flight controlactuation system of an aircraft, as well as the engine fuel systemdescribed hereinbefore. A scheme of this type is illustrated,diagrammatically, in FIG. 2. In this scheme, high and low pressurehydraulic manifolds 50, 52 are connected to respective inputs of acontrol valve 54. The control valve 54 is operable to control the fluidpressure within a line 56 by controlling the connection of the line 56to the manifolds 50, 52. The control valve 54 is mechanically actuated,and a drive input thereof is connected to a rotatable drive member 58located within, in this case, the high pressure manifold 50 such thatrotation of the drive member 58 controls the setting of the controlvalve 54 and thereby controls the fluid pressure within the line 56. Itwill be appreciated that a system of this general type may have a widerange of applications. A number of other modifications and alterationsare possible without departing from the scope of the invention.

1. A control system comprising a manifold, at least one valve deviceoperable to control the delivery of fluid from the manifold, and a drivemember located within the manifold and rotatable to control theoperation of the at least one valve device.
 2. A system according toclaim 1, wherein the system comprises part of a fuel system, themanifold comprising a fuel manifold from which fuel is delivered, inuse, via the valve devices.
 3. A system according to claim 1, whereinthe manifold further houses at least part of an input gear arrangementwhereby the drive member is rotated.
 4. A system according to claim 3,wherein an input drive shaft is provided to transmit rotary motion froma motor to the drive member and/or input gear arrangement.
 5. A systemaccording to claim 4, wherein the input drive shaft is located within afuel supply line whereby fuel is supplied to the manifold.
 6. A systemaccording to claim 4, wherein the input drive shaft passes through aseal arrangement into the manifold and/or input gear arrangement.
 7. Asystem according to claim 4, wherein the motor is an electrically drivenmotor.
 8. A system according to claim 4, wherein the motor comprises ahydraulic motor driven using pressurised fuel.
 9. A system according toclaim 1, wherein the manifold houses a series of further drive members,and gear arrangements arranged to form a drive train.
 10. A systemaccording to claim 9, wherein the drive train is in the form of acontinuous loop.
 11. A system according to claim 9, wherein each geararrangement is arranged to transmit rotary motion to one or more of saidvalve devices.
 12. A system according to claim 1, further comprising asensor to provide an output signal representative of the operating modeof the valve devices.
 13. A system according to claim 1, wherein thereis a continuous flow of fuel through the valve devices at all engineoperating conditions, in use, thereby providing a means of maintainingthe temperature of the valve devices at an acceptable level.